The only way to improve the reception of FM-signals or particularly of stereo FM-signals under disadvantageous receiving conditions is to amplify the antenna signal. This should be made directly at the antenna, since the loss is increased meter by meter of any cable. In most cases higher line attenuations can be expected than usually calculated. Even receivers with an additional noise figure of zero do not show any improvements of the signal-to-noise ratio becomes too low because of a long transmission line. Therefore it is practically useless to require extremely low noise figures only for the receivers.
To avoid interferences of signals received from stations of other bands it is propitious to amplify the FM-band only. The band amplifier shown in Fig. 1.3 is connected directly to the 60 ohm output of the FM-antenna, i. e. it is placed at the top of the antenna pole. The matching is achieved by the input band-pass connected to the base of transistor BFT12, being a typically linear silicon transistor for broadband amplifiers. The output filter matched accordingly to a 60 ohm coaxial line is connected to the collector. The operating voltage of 15 V can be supplied by the coaxial line.
- Power gain Gp = 22 db
- Noise figure F = 3.5-4.0 db or 2.2-2.5 KT0
- Input and output reflexion coefficient |r1| and |r0| <= 0.3
- dim(60db) at Vout = 680 mV
- dim(50db) at Vout = 1000 mV
Optimum operating point of minimum intermodulation
Ic =~ 80 mA Vce =~ 7-7.5 V
Supply voltage 15 V
Vogt coil former, ordering code: Sp 3.5/16.6-2048C
- L1 : 5 turns Cu 0.6 mm \o
- L2 : 3 turns Cu 0.6 mm \o
- L3 : 3+2 turns Cu 0.6 mm \o
Choke Ch1 = Ch2: 20 turns Cu L 0.3 mm \o, cross section of winding = 4 mm
Antenna-amplifier with BFT 12 for FM-range
from Design Examples of Semiconductor Devices – Siemens
This site is a free non-profit repository of materials from GAP/R George A Philbrick Researches, the company that launched the commercial use of the Operational Amplifier in 1952.
The Philbrick Archive and Operational Amplifier
The first commercial Operational amplifier was the K2-W op-amp. It was based on the amplifier used in the Philbrick modular Analog-Computor “black boxes “. That amplifier’s basic circuit architecture, in turn, was probably inspired by an earlier amplifier designed by Loebe Julie (Dan Sheingold and Bob Pease, thanks for helping me with this information). The K2-W Operational Amplifier entered the commercial market in 1952.
Bob Pease’s desk circa 1970 at Teledyne-Philbrick, as photographed by student intern Stu Brennan.
The fig. 6.2 shows the circuit of a regulated power supply for +/- 15 V and 5 A. The output voltages are adjustable between 12 and 17 V.
A tape-wound core transformer is used. It offers a better power-to-volume ratio than conventional ones with laminated cores. The voltage control is achieved by two series transistors, connected in parallel, and by the opamp TAA 761, which acts as control amplifier. For the negative voltage the ground potential serves as reference level for the desired-to-actual value comparison.
The voltage is adjusted by the potentiometers P1 and P2, whereby the center tap of P2 is set firstly to 0. Then both output voltages can be adjusted symmetrically through P1 (range between 12 V and 17 V, for instance).
NPN power-transistors are used as series-control components for the positive as well as negative voltage. Since two transistors 2N3055 have to be connected in parallel for each output voltage, 0.22 ohm resistors are inserted in their emitter leads to achieve a symmetrical load splitting.
Mains voltage …. 220V ±15% 50Hz
Output voltages …. ±15V (adjustable from 12 to 17V)
Max. output current …. 5A each
Max. ambient temperature …. 50 deg C
Tape-wound core …. 2xSE 130a
Primary windings (220 V) …. n1 = 490 turns, d = 1.0 mm o/
Secundary windings …. n2 = n3 = 50 turns, d2 = d3 = 1.8 mm o/
Ordering code …. B71725-A130-A2
Thermal resistance of heat sinks
for each transistor 2N3055 …. Rth </= 2.5 K/W
for each transistor BD234 …. Rth </= 23 K/W or
for each transistor BDX27 …. Rth </= 38 K/W
Power Supply Circuits – Voltage regulator ± 15 V/5 A
from Design Examples of Semiconductor Devices – Siemens – 1974/75
Did you know ?
Siemens Semiconductors was spun off on April 1 1999 to form a separate legal entity Infineon Technologies AG
for Information about these pages and purpose, see About Olden Circuits